Uncoated razor blades, despite their sharpness, cannot be employed for shaving a dry beard without excessive discomfort and pain, and it is as a practical matter necessary to employ with them a bear-softening agent such as water and/or a shaving cream or soap. The pain and irritation produced by shaving with uncoated blades are due to the excessive force required to draw the cutting edge of the blade through the unsoftened beard hairs, which force is transmitted to the nerves in the skin adjacent the hair follicles from which the beard hairs extend, and, as is well known, the irritation produced by excessive pulling of these hairs may continue for a considerable period of time after the pulling has ceased. Blade coatings were developed to solve these shortcomings.
Granahan et al., U.S. Pat. No. 2,937,976, issued May 24, 1960, describes a "coated" blade which provides a reduction in the force required to cut beard hair. The coating material consists of an organosilicon-containing polymer which is partially cured to a gel which remains adherent to the blade. Although these coated blades met with considerable commercial success, the coatings were not permanent and would wear off relatively quickly.
Fischbein, U.S. Pat. No. 3,071,856, issued Jan. 8, 1963, describes fluorocarbon-coated blades, particularly polytetrafluoroethylene-coated blades. The blades may be coated by (1) placing the blade edge in close proximity to a supply of the fluorocarbon and subsequently heating the blade, (2) spraying blade with a fluorocarbon dispersion, (3) dipping the blade into a fluorocarbon dispersion or (4) by use of electrophoresis. The resulting blade was later heated to sinter the polytetrafluoroethylene onto the blade edge.
Fischbein, U.S. Pat. No. 3,518,110, issued Jun. 30, 1970, discloses an improved solid fluorocarbon telomer for use in coating safety razor blades. The solid fluorocarbon polymer has a melting point between 310.degree. C. and 332.degree. C. and has a melt flow rate of from 0.005 to 600 grams per ten minutes at 350.degree. C. The molecular weight is estimated to be between 25,000 and 500,000. For best results, the solid fluorocarbon polymer is broken down to 0.1 to 1 micron particles. The dispersion is electrostatically sprayed onto stainless steel blades.
Fish et al, U.S. Pat. No. 3,658,742, issued Apr. 25, 1972, discloses and aqueous polytetrafluoroethylene (PTFE) dispersion containing Triton X-100 wetting agent which is electrostatically sprayed on blade edges. The aqueous dispersion is prepared by exchanging the Freon solvent in Vydax brand PTFE dispersion (PTFE+Freon solvent), distributed by E. I. DuPont, Wilmington, Del., with isopropyl alcohol and then exchanging the isopropyl alcohol with water. Example 1 discloses an aqueous PTFE dispersion containing 0.4% PTFE and 0.1% triton X-100 wetting agent.
Trankiem, U.S. Pat. No. 5,263,256, issued Nov. 23, 1993 (Docket No. 7951 ) discloses on an improved method of forming a polyfluorocarbon coating on a razor blade cutting edge comprising the steps of subjecting a fluorocarbon polymer having a molecular weight of at least about 1,000,000 to ionizing radiation to reduce the average molecular weight to from about 700 to about 700,000; dispersing the irradiated fluorocarbon polymer in an aqueous solution; coating said razor blade cutting edge with the dispersion; and heating the coating obtained to melt, partially melt or sinter the fluorocarbon polymer. Although these coatings adhere well to the blade edge it is very difficult to form acceptable aqueous dispersions without agitation or stirring.
Trankiem, U.S. patent application Ser. No. 08/232,197, filed Apr. 28, 1994 (Docket No. 4210) discloses a method of forming a polyfluorocarbon coating on a razor blade cutting edge comprises subjecting a fluorocarbon polymer having a molecular weight of at least 1,000,000 in dry powder form to ionizing irradiation to reduce the molecular weight of the polymer forming a dispersion of the irradiated polymer in a volatile organic liquid, spraying the dispersion on to a razor blade cutting edge and heating the coating obtained to sinter the polyfluorocarbon. The polyfluorocarbon preferably is polytetrafluoroethylene and irradiation preferably is effected to obtain a telomer having a molecular weight of about 25,000. Although these coatings adhere well to the blade edge it must be agitated to form acceptable dispersions in many volatile organic liquids without agitation and, in general, these solvents are not recommended due to their potentially adverse affect on the environment. (i.e. They are currently listed as hazardous volatile organic compounds (VOC's)).
An object of the present invention is to provide an environmentally- friendly method of coating razor blade edges with polyfluorocarbons, particularly polytetrafluoroethylene. Specifically, it is an object of the present invention to eliminate chlorofluorocarbon solvents and volatile organic solvents from the blade coating process.
It is also an object of the present invention to provide a razor blade cutting edge which produces substantially equal cutting and wear characteristics as chlorofluorocarbon dispersion-coated blades.
Another object of the present invention is to provide an environmentally-friendly method of laying down a homogeneous polyfluorocarbon coating on the cutting edge of razor blades.
And another object is to provide a method of dispersing the polyfluorocarbon particles in a blade-coating feed stream which requires no stirring or additional agitation.
Yet another object of the present invention is to provide an improved dispersion of polyfluorocarbon particles for use in blade-coating operation.
These and other objects will be apparent to one skilled in the art from the following: